Graphical user interfaces are used for the interaction between a user and computer. They represent a virtual control and display panel through which the user transmits commands or information to the computer, the computer in turn signaling back the receipt of these commands and information and/or the response thereto. For the operation and rapid navigation of the interaction, the control and display objects, such as text boxes, menus, selection lists, buttons, icons, etc. can be used. For example, pop-up menus are very popular in many interfaces for executing various groups of computer commands. The computer may display a pop-up menu over a display screen, and the user can then select and execute one of the commands contained in the pop-up menu.
These pop-up menus can be used in projector-camera systems. Cameras are often combined with projectors to form projector-camera systems, or procam systems. As a projector projects an output image on a display surface, a camera acquires an input image of the output image. Pop-up menus can be displayed on the output image over the display surface.